Moderately increased hemolysis in newborn infants with hyperbilirubinemia of unknown etiology.

Serial determinations of carboxyhemoglobin (COHb) levels were performed in full-term newborn infants during the first few days of life and their mothers. A close correlation was found between COHb in the mother and that determined in the cord blood. The correlation between COHb in the mother at delivery and that found in the neonate disappeared after 48 h of life. The determination of COHb after this period demonstrated significantly higher values of COHb levels in jaundiced neonates compared with normal infants. Determinations of erythrocyte age-dependent enzyme activities carried out at birth and after 5 days of life did not demonstrate any significant difference between the mean values in jaundiced and normal infants. However, the normal infants demonstrated a decrease of glucose-6-phosphate dehydrogenase and pyruvate-kinase activities from birth to the 5th day which is not appreciable in neonates with hyperbilirubinemia of unknown etiology. The results are discussed in relation to the role of hemolysis in neonatal hyperbilirubinemia.